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http://hdl.handle.net/11375/8561
Title: | Magnetic ordering of Erbium and UNi₂Si₂ by neutron scattering |
Authors: | Lin, Hong |
Advisor: | Collins, M. F. |
Department: | Physics |
Keywords: | Physics;Physics |
Publication Date: | Nov-1991 |
Abstract: | <p>The magnetic ordering has been studied in UNi₂Si₂ and erbium single crystals by elastic neutron scattering. Abundant results are given regarding the magnetic structure, magnetic phase transitions, and the effect of a magnetic field on these properties. Three ordered phases are observed in UNi₂Si₂. They have been determined to be an incommensurate longitudinal spin density wave with a magnetic wave vector around q = 0.74c* in the high temperature phase, a simple body-centred antiferromagnet in the intermediate temperature phase, and a square wave in the low temperature phase. This square wave can be viewed equivalently as a longitudinal spin density wave with q = 2/3c* superimposed on a ferromagnetic component. Hysteresis and sample dependence are observed in the low-temperature phase transition. The two lower temperature phase transitions are both first order. The transition to paramagnetism is second order with a critical exponent β=0.35±0.03. When a magnetic field is applied along the c axis, the intermediate temperature phase is destabilised and disappears above a field of 3.5T. Although there is no new phase induced by the field, there exists a reentrant point where the three ordered phases can coexist. Erbium has three distinct ordered phases: the cone phase at low temperatures, the c-axis modulated (CAM) phase at higher temperatures, and the intermediate phase with moments modulated both along c and perpendicular to c. Within these phases the modulation of the moments may lock in to the lattice. The observed weak harmonics of the wave vector q in the basal plane for the cone phase and the q = 1/4c* structure in the intermediate phase can be explained by a basal-plane spin slip model. The effect of magnetic field along the c axis on the magnetic structure is to stabilise the cone phase and to destabilise the intermediate phase. A new lock-in structure with q = 1/4c* in the cone phase is induced by fields above 1.8T. The presence of the field also stabilises the lock-in structure with q = 2/7c* in both the intermediate and the CAM phases.</p> |
URI: | http://hdl.handle.net/11375/8561 |
Identifier: | opendissertations/3757 4774 1709041 |
Appears in Collections: | Open Access Dissertations and Theses |
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fulltext.pdf | 2.33 MB | Adobe PDF | View/Open |
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